1. Field of the Invention
The present invention relates to an ultrasonic diagnostic equipment which transmits ultrasonic pulses into a sample so as to scan the interior of the sample, and which receives reflected waves from the sample, thereby to acquire the motion information of a tissue on the basis of the image of the interior of the sample, and a control method for the ultrasonic diagnostic equipment.
2. Description of the Related Art
An ultrasonic diagnostic equipment noninvasively obtains the tomographic image of a soft tissue in a living body, from the surface of the body by an ultrasonic pulse echo method. The ultrasonic diagnostic equipment transmits ultrasonic waves from an ultrasonic probe into a sample, it receives reflected waves created by the mismatching of acoustic impedances within the sample, by the ultrasonic probe so as to generate a reception signal, and it images the interior of the sample on the basis of the reception signal.
As compared with other medical image equipment, the ultrasonic diagnostic equipment has the following merits: By way of example, the ultrasonic diagnostic equipment is small-sized and inexpensive. It affords a high safety without exposure to X-rays etc. It is capable of blood flow imaging. This ultrasonic diagnostic equipment is employed for the diagnoses of, for example, the heart and the abdomen, and it is extensively utilized in urology, obstetrics and gynecology, etc. It has been known that the ultrasonic diagnostic equipment is useful for the diagnosis of the heart. It is very useful to objectively and quantitatively estimate the function of the tissue of the living body, such as a cardiac muscle.
As a remedy which is recently spotlighted, there is mentioned a cardiac resynchronization therapy (CRT) for the patients of serious cardiac failure. It has been attempted to employ the ultrasonic diagnostic equipment for the quantitative estimation for deciding the applicability of the cardiac resynchronization therapy or for deciding the effect of the medical treatment.
The cardiac resynchronization therapy will be briefly explained. The patient of serious cardiac failure often accompanies the contraction dyssynchrony of a cardiac wall motion. The heart is being moved by the conduction of electric signals. An intraventricular conduction disturbance sometimes arises in the patient of the serious cardiac malady. The intraventricular conduction disturbance is the occurrence of a deviation in a sequence in which the electric signals moving the cardiac muscle are conveyed. In a ventricle in which the electric signals ought to be conveyed substantially simultaneously over the entirety, the intraventricular conduction disturbance sometimes develops a part to which the electric signal is conveyed earlier and a part to which the electric signal is conveyed later, on account of the deviation. As a result, the contraction of the cardiac wall is not synchronized, and the heart fails to pump out blood sufficiently, to fall into the state of the cardiac failure.
The cardiac resynchronization therapy is the medical treatment in which an electric signal is artificially issued to such a disturbance, whereby the sequence of the electric signals to be conveyed to the heart is adjusted to assist in the pump function of the heart. Concretely, the medical treatment is done by embedding a pacemaker under the skin of the breast. The cardiac resynchronization therapy has already been performed for a large number of patients, and dramatic improvements in the symptoms have been verified.
On the other hand, there are cases as to which the improvements in the symptoms are not observed even when the cardiac resynchronization therapy is applied. The cases are cardiac failure ones. The patients of such cardiac failure cases have been verified to amount to about 30% of all patients. This is because whether or not the cause of the cardiac failure cases is the contraction dyssynchrony cannot be exactly judged.
In the present situation, the application criteria of the cardiac resynchronization therapy are stipulated to be less than 130 msec in the QRS width of an electrocardiogram waveform and to be 35% in the left ventricular ejection fraction (EF). In accordance with the criteria, patients who suffer from the cardiac failure, but who do not suffer from the contraction dyssynchrony are also included.
Therefore, there has been developed a technique which is intended to extract only the contraction dyssynchrony by a quantitative estimation method employing the ultrasonic diagnostic equipment. The technique is disclosed in, for example, the official gazette of JP-A-10-262970. The official gazette of JP-A-10-262970 discloses to detect the motion velocity of a cardiac muscle (cardiac wall) by a Doppler method, and to calculate and analyze this motion velocity. The technique can automatically detect the peaks of the changes-with-time of motion velocities, displacements or the likes at the pluralities of parts of the cardiac muscle. In addition, the technique calculates time periods from a predetermined cardiac phase till arrivals at the individual peaks and then colors the ultrasonic image of the cardiac muscle in accordance with the time periods. Thus, the differences of the motion states of the whole cardiac muscle are outputted as color images. The differences of motion timings at the respective parts of the cardiac muscle can be imaged.
The ultrasonic diagnostic equipment has realized to image, not only a structure within a living body, but also the movement velocity of a tissue, by a tissue Doppler method. The tissue Doppler method measures the velocity of a part of intense reflection and comparatively slow movement, such as cardiac wall, and it presents a two-dimensional color display. In recent years, techniques for obtaining clinically more important information have been proposed by applying the function of imaging the movement velocity of the tissue by the tissue Doppler method. The techniques are, for example, the imaging of movement timings as employs the movement velocity distribution image of the tissue, velocity gradient imaging, displacement imaging, strain imaging, and tissue tracking which employs angular corrections.
The imaging of the movement timings as employs the movement velocity distribution image of the tissue performs the color coding of time periods in which the tissue movement velocities of individual pixels arrive at a certain threshold value or at peaks, by employing the movement velocity distribution image of the tissue as obtained by the tissue Doppler method. Thus, the movement timings of the tissue are imaged. This imaging is disclosed in, for example, the official gazette of Japanese Patent No. 3,187,008.
The velocity gradient imaging acquires a local velocity gradient in such a way that the velocity difference of two points spaced a predetermined distance, as to a movement velocity distribution obtained by the tissue Doppler method, is divided by the distance between the two points. In addition, this imaging acquires such local velocity gradients at the large number of points of the image so as to display the acquired gradients as an image.
The displacement imaging computes the quantity of the movements of the tissue by integrating values obtained in such a way that the velocity values of individual frames included in a predetermined time period are multiplied by an interframe time difference, as to a movement velocity distribution obtained by the tissue Doppler method.
The strain imaging obtains the strain distribution image of the tissue by employing the movement quantity distribution image obtained by the displacement imaging, or the velocity gradient image.
In obtaining the displacement image or the strain image, an integration process employing the values of a plurality of frames is required. As is usually considered, the integration of the values of the same pixels of the plurality of frames does not become the integration of the value of the same tissue as to the moving tissue. The tissue tracking which employs the angular corrections need to integrate the values while tracking the movements of the tissue.